1. Technical Field
The present disclosure generally relates to coupled vehicles, for example tractor trailer combinations, and more particularly with enhancing fuel economy of coupled vehicles.
2. Description of the Related Art
A large volume of traffic employs two or more vehicles that are physically coupled together. Such vehicles may be employed for moving freight, people, and/or animals.
A ubiquitous example of coupled vehicles is that of the tractor-trailer or semi-trailer combination, which employs a tractor, sometimes referred to as a primary mover, coupled to pull one or more trailers. Such tractor-trailers or semis come in a large variety of forms and are typically used to move freight over relatively long distances. The tractor is the drive mechanism that pulls or pushes the trailer. The tractor includes the engine, typically an internal combustion diesel engine, a transmission and drive wheels. The tractor typically includes a cab where the driver or operator sits to operate the tractor. The tractor may also include a sleep cab which provides accommodations for the driver or operator when not in motion. The trailers are typically removably coupled to the tractor via a coupler such as a fifth wheel carried by the tractor, or less commonly via an automatic coupling. A semi-trailer typically does not have a front axel, relying on the tractor for support of a portion of the trailer's weight, and may have one or typically more rear axels. In some instances, a tractor may pull multiple trailers. In such a case, the following trailer(s) may not have front axels so may rely on the proceeding trailers for supporting a portion of the trailer's weight. Trailers come in a large variety, for example box, bus, curtain side, flatbed, “low boy”, refrigerated or “reefer”, tanker, dry bulk, car carrier, drop deck, “double decker” or sidelifter.
Another example of coupled vehicles are railroad trains. Rail road trains typically include one or more locomotives that pull a number of cars along a set of tracks. The cars may include passenger cars and/or freight cars. The freight cars can take a large variety of forms, similar in some respects to the various types of trailers.
Tractor-trailers or semis are increasingly being used to move containerized cargo. Such use of tractor trailers may conveniently cooperate in conjunction with ships (e.g., ocean going container ships, barges) and/or railroad trains. For instance, containers may arrive by ship from overseas. Tractor-trailers may move some of the containers over roads to warehouses or to retail locations. Tractor-trailers may move some of the containers to rail yards. Some containers may be moved via railroad trains, and subsequently moved to a desired location via tractor-trailers.
Coupled vehicles typically must be capable of operating in a variety of environments. For example, coupled vehicles must be capable of carrying loads at relatively high speed over long distance. For instance, tractor-trailer combinations typically must be able to haul freight over highways such as toll roads or freeways within some posted speed limit. Such highways are typically relatively straight over long distances, and do not require much turning or maneuvering. Such tractor-trailers typically must also be able to haul freight over surface streets at much lower posted speed limits. Travel over surface streets typically requires higher maneuverability than travel over highways, often requiring essentially right angle turns in relatively confined spaces or navigating steep elevational changes.
Fuel efficiency is typically an important concern when operating coupled vehicles. A large portion of the cost of moving freight or people is attributable to fuel costs. Fuel efficiency tends to decrease as speed increases. Fuel efficiency while traveling on highways is particularly a concern since the average speed is higher than on surface roads and, for most operations, more time is spent on highways than on surface streets.
Numerous approaches have been suggested for increasing fuel efficiency of vehicles. These approaches typically employ ferrules, fairings, cowlings, air dams, deflectors, and/or spoilers located at various locations, for instance on a front of the tractor or over a roof of the tractor. Some approaches for increasing fuel efficiency specifically address the problem created by the fact that there is a gap between the tractor and trailer. Some of the approaches for increasing fuel efficiency are illustrated in U.S. Pat. Nos. 3,697,120; 3,711,146; 3,934,923; 4,036,519; 4,750,772; 5,078,448; and 6,585,312.